It has hitherto been necessary in heat-transfer tubes of heat-exchangers to periodically eliminate scales, such as an incrustation or rusts, deposited thereon during operation and to prevent the heat-transfer tubes from their reduced performance of heat-transfer and from their corrosion.
For this purpose, heretofore, an automatic cleaning apparatus has been known, in which a cleaning brush is mounted to a receiving frame arranged at either end of each tube while a water flow into the tube is switched to reciprocate the brush therein (Japanese Patent Publication No. 44-29929). With this type of the automatic cleaning apparatus, however, there have been several disadvantages in that the forcible switching of the water flow is necessary, that an opening in the receiving frame designed for receiving the cleaning brush leads to a loss of the water flow, and that foreign substances may be deposited on the inner tube surfaces.
In another method, spongy balls are placed and floated on a heat-exchanging water and are passed through the heat-transfer tube for its cleaning. This method, however, requires a special equipment for introducing and recovering the spongy balls, resulting in a larger space for accommodating the equipment and ensuring uniform distribution of the balls. Further, operational control for determining and supplementing the loss of the balls is very troublesome. In order to solve such problems, there has been proposed a cleaning system for circulating the balls (Japanese Utility Model Publication No. 52-35584) which, however, is merely designed for providing an ideal condition for the cleaning through removal of water from the balls and refill of sufficient water for its replacement and thus cannot provide a basic solution of the problems.
Accordingly, an object of the invention is to provide a reliable and efficient method for cleaning a plurality of inner heat-transfer tube surfaces in a heat-exchanger, which may be performed automatically without disturbing its operation.